Everyday Health
When you have multiple sclerosis (MS), your body’s immune system attacks your central nervous system. This causes inflammation that damages the protective myelin sheath that normally covers the nerve fibers in the brain, spinal cord, and optic nerve, as well as the nerve fibers themselves, according to the National Multiple Sclerosis Society (NMSS).
But no one knows exactly what triggers the immune system to attack the central nervous system. Most experts believe it occurs when a person with a genetic predisposition to MS is exposed to certain environmental conditions, such as a low vitamin D level, smoking, or the Epstein-Barr virus, notes the NMSS.